Circulating solids dispersed in a liquid



June 15, 1965 Ri H. ovERcAsHu-:R ETAL 3,189,080

CIRGULATING SOLIDS DISPERSED IN A LIQUID Filed Dec. 14, 1961 POLYMERSOLUTION INVENTORS:

ROBERT H. OVERCASHIER CHARLES E. SANBORN BY'- M/f/ THEIR ATTORNEY 3189,08t9 CERCULATWG SGLHS DESPERSED iN A LlQUiD Robert lil. @vereashierand Charles E. Sanborn, Walnut Creek, Calif., assign-.ors to Shei GiiCompany, New York, N.Y., a corporation of Deiaware Filed Dec. 14, 1961,Ser. No. 159,379 5 Ciaims. (Cl. Ti59-25) The invention relates tocirculating a slurry of solids in a liquid of higher density than thatof the solids to' eifect prolonged contact between the solids and theliquid and to maintain the solids in a dispersed condition within theliquid for any purpose. One such purpose is to cause volatileconstituents of the solids to be vaporized. The invention is, forexample, applicable to effecting prolonged contact between syntheticelastomer `polymer crumbs (sometimes called rubber crumbs) with hotwater to afford time for volatile hydrocarbon solvent contained in thecrumbs to vaporize; however, the invention is not restricted to thisapplication.

A specific example of application is the coagulation of olefin polymers,such as polybutadiene, from a solution in a volatile hydrocarbon solventby mixing the solution with steam and hot water (usually condensate) toform polymer crumbs and vaporize the solvent, which escapes from thesurface of the water. A part of the solvent remains in the porous,low-density crumbs, either oecluded or in solution therewith, andprolonged contact of the crumbs with the hot water is required to effectfurther flashing of the solvent. Steam is often sparged into the waterto supply lheat. During this prolonged contact, it is important that thecrumbs be kept separated and dispersed in the water and therebyprevented from y United States Patent O M forming-larger masses oragglomerates, from which the solvent escapes more slowly. Mere agitationof the liquidcontained in an unpartitioned vessel has been ineffectiveto insure separated movement of the crumbs.

A particular diiculty encountered in such operations is that of insuringentrainment of the solids in the liquid because they tend to float onthe surface, where they remain in contact with each other to formagglomerates. Excessively high power expenditures are necessary to carrythe crumbs downward from the liquid surface by means of submergedagitators operated in an unpartitioned vessel.

To draw the floating solids from the liquid surface it was found to benecessary to provide a well-defined down-flow channel, and to this endthe vessel was subdivided by a vertical partition, such as a draft tube,into 11p-flow and down-flow zones which are in intercommunication at thetop and bottom, and Vmeans to induce iiow, such as an impeller, wereprovided in at least one of these channels to cause circulation.Although effective in certain systems, this still requires excessivelyhigh circulation rates, and therefore, high expenditures Vof power whenthe disparity in density between the solid .and liquid is great and/orwhen a large amount of gas ascends, eg., due to escape of vaporizedsolvent or admission of steam.

It is, therefore, an object of this invention to provide an improvedapparatus for promoting the circulation of solids in dispersion thereofin a liquid of greater density whereby the tendency for the soilds tofloat at the surface is overcome. Ancillary thereto, it is an object toremove volatile constituents from solid particles by prolongedcirculation of a slurry thereof in a heated liquid.

A further and specific object is to form an aqueous slurry of syntheticelastomer polymer from a solution of the polymer in a volatilehydrocarbon solvent and to free the resulting polymer crumbs from thesaid hydrocarbon solvent by circulating the said slurry within acontaining i ananas Patented June 15, 1965 vessel while maintaining thecrumbs separated from each other. v

Still another object is to improve the entrainment of light solids, suchas synthetic elastomer crumbs, in a relatively denser liquid, such aswater, which liquid is contained in a confining vessel and circulatedthrough upflow and down-flow zones which are separated` by a partitionbut are in intercommunication atthe bottom and the top, by providingbaflies to accelerate the flow of the liquid at the surface suciently todrag the floating solids down into the down-flow zones.

ln summary, it was found thatnvaporization of the volatile` constituentsfrom solids, such as a hydrocarbon solvent from synthetic elastomercrumbs, can be effected by circulating a dispersion of such solids in aheated liquid, eg., hot water, within a confining vessel successivelythrough up-flow and down-flow zones which are in intercommunication atthe bottom and at the top below the surface of the liquid and insuring avelocity at the liquid surface which is great enough to entrain thesolids in the liquid entering the down-How channel. Steam may beintroduced together with the feed stream and/or sparged into the body ofliquid.

According to a further feature the said liquid velocity at the surfaceis brought about by means of a substantially horizontal baiie at the topof the partition between the up-iiow and down-flow zones, said baiiiebeing submerged a small distance below the liquid surface to obstructpartially the area of at least one of said zones and provide a shallow,horizontally elongated ow zone extending between said other zones,whereby the liquid must ow with high velocity at the surface and entrainthe solids.

The invention will be further described with reference to theaccompanying drawing forming a part of this specication and showing apreferred embodiment, where- 1n: v

FIGURE l is an elevation-view of a series of circulating vessels, bothconstructed in accordance with the invention and suitable for effectingvaporization of volatile material from solids;

FIGURE 2 is a sectional view of the lower part of one of the vessels,shown to an enlarged scale and taken on a ,vertical line E Zof FIGURE 3;and

fer pipe 7, it being understood that any suitable number Y of suchvessels may be used. The vessels are of like construction except for theinlet arrangements, but need not be of the same size. Each vessel may beclosed, asshown, to facilitate recovery of solvent vapors and to permitoperation at superatmosphcric pressure. It contains a partition in theform of a cylindrical draft tube 8 mounted vertically and coaxially inspaced relation above the vessel bottom by radial baffles 9, it?, todenne a central down-dow channel lit and an annular up-tiow channel l2.VIn thepreferred embodiment shown the horizontal area or the latterchannel exceeds that of the former. To induce circulation an impeller ormarine propeller 13 is mounted within the tube at `the end of a shaft14, which is driven by suitable drive means, such as an electric motori5. The tube advantageously contains a plurality, eg., four, verticalbaffles 16 and the vessel may containisimilar baffles 17, these bafesbeing for the pur'- pose of reducing swirling motion of the liquid. Aliquid slurry or a fluid stream from which a slurry of solids dispersed`in a liquid can be formed is introduced into the iirst vessel 5 via aninlet pipe 1S and vapor s discharged therefrom through a vent pipe i9,which may be maintained at any desired pressure and lead to a solventrecovery system, not shown. The liquid is maintained to a predeterminedlevel above the draft tube by any suitable means, such as an overilowweir pipe 20 which is, in the first vessel, connected to the transferpipe 7. When the two vessels are operated at greatly different pressuresa pressure-reducing valve 21 may be provided in the transfer pipe 7. Theoverilow weir pipe 20 of the second vessel leads to a discharge pipe 22.The vessels 5 and 6 may be of different capacities to afford differentresidence times. Thus, as shown, the weir may be higher in the vessel 6to give a larger residence time.

When liquid is circulated downward through the central channel 11 by thepropeller 13 and upwards through the channel 12 there is a strongtendency for light solids to iloat and to accumulate as a more or lessstagnant mass, principally near the vessel wall. Only at extremely highliquid ilow rates can these -solids be entrained in the liquid whichilows down through the draft tube. To overcome this objectionableoccurrence, there is provided an annular baille 23 at the top of thetube, extending outwardly over outer channel so as to obstruct a partthereof. Typically the baffles cover from 0.2 to 0.8 of the area of thelarger channel. Although the baille is shown, in the preferredconstruction, to extend only over the upilow channel this is notrestrictive of the invention. Similarly, the use of a smaller area forthe downlow channel is not an absolute requirement but is preferable tofacilitate the action of the propeller. To avoid the formation of apocket beneath the baffle in which sticky solids may otherwiseaccumulate and to improve the flow pattern it is desirable to mount afrusto-conical baille 24 about the draft tube, the top end of thisbaille being joined to the edge of the baille Z3. The flow area of theouter channel is thereby gradually diminished toward the top.

lt should be noted that the level of the baille 23 and the top of thedraft tube is only a short distance below the surface of the liquidmaintained in the vessel by the overilow weir pipe 20 and indicated atL. Typically, this distance is between about 0.5 to 1.5 of the radialextent of the annular width of the opening outside the baille 23, so asto deilne above that baille a shallow ilow zone for the ilow of liquidinwards with high velocity.

When applied for coagulating synthetic elastomer polymer from ahydrocarbon solution, said solution is supplied by a pipe 25 and steamfrom a supply pipe 26 is injected through a branch pipe 27 at a ratecontrolled by a valve 2.8 to cause ilashing of the solvent andcondensation of the steam. If desired, water may be introduced into thestream from a pipe 29 through a valve 30. Steam is admitted to the lowerpart of the Vessel 6 from the pipe 26 via a valve 31 and to sparger 32.It is evident that such a sparger may also be provided for the vessel 5.

Example To form an aqueous slurry of polymer crumbs, a solution ofpolymerized butadiene in a solvent consisting of 20% by weight benzeneand 80% C4 hydrocarbons, principally butene, the polymer contents insaid solution being about 10% by weight, is ilowed at ambienttemperature through the pipe 25 at a pressure of 55 lbs. per sq. inchgage and is mixed with saturated steam (303 F.) at the same pressureadmitted through the pipe 27 in amount 2 parts by weight of saidsolution to 1 part of steam. Water is also admitted from the pipe 29 inamount to cause the resultant slurry in the vessel 5 to contain abouttwo to three parts by weight of rubber crumbs for 100 parts of water,which iills the vessel to the level of the overilow pipe 20. The steamcauses rapid vaporization of the hydrocarbon solvent, which passes oilinto the space above the liquid and the polymer coagulated in the formof porous crumbs. This causes most of the steam to condense. The crumbs,still containing large amounts of the solvent, typically from 10 to 25%,are maintained in contact with the water by operating the propeller 13so as to induce a downilow of the resultant slurry of crumbs in hotwater through the draft tube 8 and an upilow in the annular channel 12.This causes additional amounts of the solvent to be vaporized to anextent dependent upon the residence time. The vaporized solvent,together with some steam, is discharged at a pressure between about 50and 53 lbs. per sq. inch gage via Ithe pipe 19.

In a preferred arrangement a series of such contacting vaporizingvessels is used in series, only two being shown for purposes ofillustration. For example, an aqueous slurry containing crumbs fromwhich over half of the solvent initially in the crumbs has beenvaporized, is obtained after a residence time of two minutes, and ispassed through the pipe 7 to the second vessel wherein additionalvaporization occurs. This vessel may be operated at atmospheric pressure(2l2 F.) and additional steam is sparged into the slurry to supply heat.The hydrocarbon solvent content of the crumbs in Ithe eilluentdischarged at 22, after a longer residence time, is typically from 0.1to 2%.

The improvements due to the use of (1) partitioned up-ilow and down-ilowzones and (2) the horizontal baille 23 are evidenced from the following:for an equivalent vaporization of hydrocarbon solvent from the polymercrumbs, the following amounts of power must be used for maintaining thecrumbs dispersed in the liquid:

(A) With an unpartitioned vessel equipped with a conventional stirrerhaving paddles: Over 200 horsepower per 1,000 gallons of slurry.

(B) With the draft tube, but without the horizontal baille: about 11 to90 horsepower per 1,000 gallons of slurry, depending on the draft tubeand propeller diameter.

(C) With the arrangement described: 4.5 horsepower per 1,000 gallons ofslurry.

An advantage of the draft tube (B) as compared to the simple vessel (A)is that it permits the propeller to be small relative to the vesseldiameter. Secondly, by making the horizontal area of the down-ilowpassage smaller, it permits high velocities therein at modest powerlevels while permitting low velocity in the up-ilow zone. Typically, thearea of the up-ilow channel is from three to fifteen times that of thedown-ilow channel. Thirdly, it permits introduction of the volatilematerial into the upilow channel (viz., the pipe 18 and the spargers 32are situated near the vessel wall), whereby the ascending vapors willnot interfere with the action of the propeller.

The advantage of the horizontal baille of arrangement (C) may beexplained as follows: When the baille 23 and cone 24 are omitted, thereis a tendency for the light polymer crumbs to iloat on the surface ofthe water, particularly near the vessel walls. This not only exposesthem to the ascending vapcrized solvent but causes them to formagglomerates from which the volatiles can escape less readily. To drawthem downward into the draft tube exceedingly high liquid velocities arerequired.

With the arrangement shown there is a rapid upward movement of theslurry about the cone 24, resulting in a liquid surface as shown by theline L in FIGURE 2. This local turbulence and rapid movement entrainsthe crumbs and carries them into the draft tube with far lower liquiddown-ilow velocity through this tube.

Although the specic example given pertained to the preparation of anaqueous slurry of polybutadiene, it is obvious that the invention is notrestricted thereto and that the physical action involved may be appliedto a wide variety of materials, which may but need not be syntheticelastomers. Regarding such elastomers, it may be noted that it is knownthat varied useful elastomers may be produced from conjugated dieneswherein the elastomers have a high content of the cis 1,4-additionproduct. The more useful of the cis 1,4-addition products are thoseprepared from isoprene and butadiene as they have properties suitablefor application where natural rubber yis used. The prior art describesthe polymeriza- E tion of conjugated dienes to produce cis 1,4-additionproducts, for example, by polymerizing isoprene with any of a largevariety of hydrocarbyl lithium catalysts, such as nabutyl lithium, amyllithium, and other normal alkyl lithiums from 2 to 10 carbon atoms. Asanother example, cis 1,4polybutadiene may be prepared with a catalystthat is the reaction product of a transition metal compound,particularly halides, of a Group lV to VIH metal and a strong reducingagent, eg., a metal compound, particularly organo-metallics, of a GroupI to Ill metal. Other classes of highly useful elastomers arerepresented by the copolymers of ethylene and propylene, which areproduced by polymerizing a mixture of the monomers with a catalystcomprising the reaction product of, for example, vanadium oxychlorideand a reducing agent of the type previously described.

These polymerizations are conducted in the presence of liquid, inert,volatile solvents, such as isopentane, hexane, gasoline, benzene,toluene, and the like, and as the polymerization proceeds the elastomerforms and remains in solution until it is to be recovered. Thecoagulation method described above is one method of recovering theelastomer and permits these liquids to be removed to the extent that theelastomer contains less than 2% by weight, eg., down to 0.1% of solvent.This high degree of removal of solvent leads to improved rubrberproducts, since the presence of solvent causes the products to blisterand weaken during vulcanization.

We claim as our invention:

1.. Apparatus for circulating a liquid slurry containing solids thattend to lloat on the surface, which comprises:

(a) an upright vessel,

(b) means for maintaining a body liquid within said vessel to a levelbeneath the top thereof,

(c) a partition situated within said vessel below said level anddefining an uptlow channel and a down- `iiow channel intercommunicatingwith each other at the bottom, Y

(d) means for inducing flow of slurry successively through saidchannels, and

(e) a substantially horizontal, essentially dat bafe extending laterallyfrom the top of said partition and situated a short distance beneathsaid liquid level to provide a shallow, elongated passageway for liquiddow from the top of the upow channel into the downow channel, forinducing strong horizontal flow and thereby entraining said solids fromthe sur- -faoe of the liquid.

2. Apparatus as delined in claim 1l wherein said channels have diiferenthorizontal areas and said horizontal baille extends from said partitionover the larger of said channels for a distance to obstruct between 0.2-to 0.8 of the area thereof.

3. In combination with the apparatus defined in claim 2, an inclinedbaille within said larger channel joined to said partition below thehorizontal baffle and exteding to the end of the horizontal baille torestrict said larger channel gradually toward the top.

4. Apparatus for devolatilizing synthetic elastomer polymer crumbscontaining volatile hydrocarbon solvent by prolonged contact with hotwater, said crumbs tending to iloat on the surface of the water, whichcomprises:

(a) a closed, upright vessel,

(b) means for admitting hot water and synthetic elastomer polymer crumbscontaining a volatile hydrocarbon solvent into said vessel to form saidcrumbs therein,

(c) means for discharging an aqueous slurry of said polymer from andmaintaining liquid within the vessel to a predetermined level below thetop,

(d) means for discharging vapor from the top of said vessel,

(e) a cylindrical draft tube situated vertically within said vessel anddening a central ow channel and an annular flow channel, said tubehaving the top thereof situated below said liquid level,

(f) impeller means within said tube for causing circulation of liquidand entrained polymer crumbs vertically successively through saidchannels, and

(g) an annular substantially horizontal, essentially flat battle plattesituated at the top of said tube a short distance below said liquidlevel and extending laterally outwardly from the tube to provide ashallow, horizont-ally elongated passageway for liquid flow from the topof one of said channels to the other, for inducing strong horizontalflow and thereby entraining said crumbs from the surface of the water.

5. In combination with the apparatus defined in claim 4, a generallytruste-conical baille situated in said one channel having the lower endthereof adjacent said tube below the top thereof and the upper endthereof a-t the edge of said horizontal batlle to reduce the horizontalarea for vertical flow in said one channel progressively toward the top.

References Cited by the Examiner UNTTED STATES PATENTS 643,794 2/00Harvey 159-27 X 861,893 7/0'7 Pool 159-25 X 975,380 11/10 Bernston259-96 1,028,086 5/ 12 AFaller 159-27 1,033,580 7/19 Hall et al. 159-271,381,673 6/21 Sherwood 259-96 Y1,461,640 7/23 Wirth-Frey 159-161,476,331 12/23 Engel 159-25 1,835,250 12/31 Webre 159-25 1,917,841 7/33Hughes et al 159-16 1,945,281 1/ 34 Leithauser 159-45 1,982,002 1,1/ 34Hatch 162-66 X 2,473,488 6/49 Hughes 159-45 X 2,495,120 1/50 Miller etal. 260-96 X 2,799,662 7/57 Ernst et al. 260-29.7 2,833,750 5/58 Vickers260-96 X 2,912,401 ll/ 59 Aldridge et al. 260-29-7 FORElGN PATENTS 31810/ 99 Austria. 1,125,321 10/56 France.

18,130 1905 Great Britain.

NORMAN YUDKOFF, Primary Examiner.

LEON l. BERCOVTZ, Examiner.

4. APPARATUS FOR DEVOLATILIZING SYNTHETIC ELASTOMER POLYMER CRUMBSCONTAINING VOLATILE HYDROCARBON SOLVENT BY PROLONGED CONTACT WITH HOTWATER, SAID CRUMBS TENDING TO FLOAT ON THE SURFACE OF THE WATER, WHICHCOMPRISES: (A) A CLOSED, UPRIGHT VESSEL, (B) MEANS FOR ADMITTING HOTWATER AND SYNTHETIC ELASTOMER POLYMER CRUMBS CONTAINING A VOLATILEHYDROCARBON SOLVENT INTO SAID VESSEL TO FORM SAID CRUMBS THEREIN, (C)MEANS FOR DISCHARGING AN AQUEOUS SLURRY OF SAID POLYMER FROM ANDMAINTAINING LIQUID WITHIN THE VESSEL TO A PREDETERMINED LEVEL BELOW THETOP, (D) MEANS FOR DISCHARGING VAPOR FROM THE TOP OF SAID VESSEL, (E) ACYLINDRICAL DRAFT TUBE SITUATED VERTICALLY WITHIN SAID VESSEL ANDDEFINING A CENTRAL FLOW CHANNEL AND AN ANNULAR FLOW CHANNEL, SAID TUBEHAVING THE TOP THEROF SITUATED BELOW SAID LIQUID LEVEL, (F) IMPELLERMEANS WITHIN SAID TUBE FOR CAUSING CIRCULATION OF LIQUID AND ENTRAINEDPOLYMER CRUMBS VERTICALLY SUCCESSIVELY THROUGH SAID CHANNELS, AND (G) ANANNULAR SUBSTANTIALLY HORIZONTAL, ESSENTIALLY FLAT BAFFLE PLATE SITUATEDAT THE TOP OF OF SAID TUBE A SHORT DISTANCE BELOW SAID LIQUID LEVEL ANDEXTENDING LATERALLY OUTWARDLY FROM THE TUBE TO PROVIDE A SHALLOW,HORIZONTALLY ELONGATED PASSAGEWAY FOR LIQUID FLOW FROM THE TOP OF ONE OFSAID CHANNELS TO THE OTHER, FOR INDUCING STRONG HORIZONTAL FLOW ANDTHEREBY ENTRAINING SAID CRUMBS FROM THE SURFACE OF THE WATER.